The video should be entirely neglected. So yes, you can define your own variables, and in particular what you call Q_total would be important for a power plant.

The video should be entirely neglected. So yes, you can define your own variables, and in particular what you call Q_total would be important for a power plant. But nobody claims that current fusion experiments are power plants, and as a matter of fact they are not power plants. The Q_total variable is entirely meaningless when talking about them!